High Speed Downlink Packet Access

Transcription

1 High Speed Downlink Packet Access Matúš Turcsány KTL FEI STU 2010

2 Data traffic characteristics Asymmetrical Bursty > 384 kbps needed Low latency

3 Reduce latency fast scheduling adaptive scheduling HARQ avoid protocol translation reduce signaling simple core architecture increase L1/L2 granularity 1) L2/L3 issues 2) small effect on L1 3) can be changed in already existing system How to Increase throughput more bandwidth higher order modulation less FEC more power more MIMO 1) mostly L1 properties 2) set by the system design/ regulation 3) harder to change in already existing system

4 What has bigger impact? Throughput increase 5000% 4000% 3000% 2000% 1000% 0% Sensitivity analysis - latency cnn.com 16% 39% 72% 226% 329% 609% 4000% 10% 20% 30% 40% 50% 60% 70% Latency decrease

5 What about UMTS R99? Design changes Channel transport physical Scheduler Frame format Modulation HARQ Functionality move towards the Node B Power control

6 Power control R99 Choose throughput Evaluate radio conditions Required cell power Circuit switched services are guaranteed Packet switched services are best effort

7 Power control - revised Unused cell power Evaluate radio conditions Power HSDPA Accept throughput No guarantee Best effort Maximize cell capacity Utilize all available power R99 Common Channels Time

8 HSDPA 3GPP Rel.5 2 ms frame format 2 ms scheduler ATDMA/CDMA CQI 16 QAM or QPSK HARQ (Chase, Incremental Redundancy) on L1 (not RLC) Fixed SF = 16 Turbo code only Fixed CRC (24 bit) No soft handover

9 Higher Order Modulation 2 bits/symbol 4 bits/symbol QPSK 16QAM 16QAM Twice the data rate compared to QPSK (used in R99) Making optimal use of good channel conditions (high C/I) Close to cell site Low speed Little or no dispersion

10 Short TTI Transmission Time Interval Reduced air-interface delay Improved end-user performance HSDPA features operate at 500 times per second 10 ms 20 ms 40 ms 80 ms Fast Link Adaptation Fast hybrid Automatic Repeat Request (ARQ) with soft combining Fast Channel-dependent Scheduling Earlier releases 2 ms

11 Code multiplexing

12 Fast Channel-dependent Scheduling Scheduling = which UE to transmit to at a given moment Basic idea: transmit at fading peaks May lead to large variations in data rate between users Tradeoff: fairness vs. cell throughput Scheduled user high data rate User 1 User 2 low data rate Time #1 #2 #1 #2 #1 #2 #1

13 Scheduling UEs send reports CQI = Channel Quality Indicator (0-30) Not explicit quality indicator, but the date rate supported by the UE

14 HSDPA Transport Channels one High-Speed Downlink Shared Channel (HS-DSCH), used for downlink data transmission, mapped to up to 15 HS-PDSCH, and is dynamically allocated every 2 msec up to four High-Speed Shared Control Channels (HS-SCCH), used for downlink control signaling, (e.g. - UE ID, HARQ, TFRC) one Associated Dedicated Channel (A-DCH) pair (UL & DL) per HSDPA user in connected state used for controlled signaling and uplink data transmission

15 HS-PDSCH

16 Hybrid ARQ

17 Hybrid ARQ Send & Wait strategy Long delays Up to 12 parallel processes Buffer memory in the UE is important

18 ARQ Loops

19 UE classes

20 3G voice or data? Relative Network Load RNC level HSDPA networks 50% at 3,6 Mbps marginal 7,2 Mbps share 310 HSDPA devices 221 HSPA networks > 30% at 7,2 Mbps 55 EUL networks 800 HSPA devices Packet data Voice Jan 07 Mar 07 May 07 Jul 07 Sep 07 Nov 07 Jan 08 Mar 08 May 08 July 08 Sep 08 Nov 08 Jan 09 Data is surpassing voice on 3G since 2 years

21 HSPA+ 64QAM (21 Mbps) alebo 2x2MIMO (28 Mbps) 64QAM a Dual-Cell (42 Mbps / 10 MHz) 64QAM a MIMO (42 Mbps / 5 MHz) MIMO a Dual-Cell (56 Mbps / 10 MHz) 64QAM a MIMO a Dual-Cell (84 Mbps / 10 MHz) 64QAM a MIMO a Q-Cell (168 Mbps / 10 MHz) 64QAM a 4x4MIMO a Q-Cell (336 Mbps / 10 MHz)

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23 Enhanced Uplink

24 Resource usage interference E-DCH R99 Intra cell Interference Inter cell Interference time

25 Design principles Multi code transmission HARQ TTI 2/10 ms Scheduling Multi-code transmission (1-4 codes) TTI = 2 / 10 ms Hybrid ARQ with Soft Combining in Node B Scheduling

26 EUL Physical Layer QPSK is used both in DL & UL, but: in DL, QPSK for each data channel in UL, every data channel is BPSK modulated UL uses 2 separate OVSF code trees! so EUL can use for example 2x SF2 & 2x SF4 Q I I branch Q branch occupied by E-DPDCHs left for control channels

27 EUL channels

28 Enhanced Uplink Channels E-DCH Dedicated Physical Data Channel (E-DPDCH) is the data transport channel. The power of the E-DPDCH is set dynamically as an offset to the DPCCH, a so called gain or beta factor, signaled with the grant messages delivered by the scheduler. E-DCH Dedicated Physical Control Channel (E-DPCCH) is used to transmit to the scheduler information about the channel conditions as seen from the UE. E-DCH Absolute Grant Channel E-AGCH a shared downlink channel that carries absolute grants. The absolute grant is sent by the scheduler to the UE giving it the information it needs to select a rate and the transmission power. E-DCH Relative Grant Channel E-RGCH is the channel carrying relative grants. Relative grants are transmitted from non-serving cells only, at the rate of one relative grant per 10 ms from each cell in the active set. E-DCH HARQ Acknowledgement Indicator Channel E-HICH a dedicated channel, carrying the binary hybrid ARQ (HARQ) acknowledgements. One E-HICH is set up to each EUL user from each cell in its active set.

29 Scheduling Node B decides at which power UE can transmit Absolute Grant from serving cell Relative Grant both from serving/non-serving cell(s) Serving cell (UP, DOWN, HOLD) dedicated to 1 UE Non-serving cell(s) (DTX, DOWN) to all UEs (overload indicator)

30 Scheduling Scheduling request (UL) Used by the UE to request more resources Absolute grant (DL) Used for large absolute changes of the data rate Relative grant (DL) UP/HOLD/DOWN UE 1 UE 2 Rate Rate Request Absolute grant Relative grants Relative Grant Request Relative Grant Absolute Grant

31 EUL UE classes cat7 16QAM = 11,5 Mbps

32 New Radio interface protocol entities DTCH DCCH DTCH DCCH MAC -d MAC -d MAC -es/ MAC -e MAC -e E-DCH FP MAC -es E-DCH FP PHY PHY TNL TNL TNL TNL UE Uu Node B Iub DRNC Iur SRNC

33 HSDPA / EUL peak rates Downlink Uplink 3.6 Mbps Mbps QAM 14 Mbps 21 Mbps 28 Mbps 42 Mbps 15 codes 2x2 MIMO Multi-carrier 4x4 MIMO Higher Modulation Combinations 12 Mbps 5.8 Mbps 2 Mbps Multi-carrier 16QAM 2 ms TTI Mbps Mbps

34 Multi-antenna systems

35 MIMO principle Array gain: Increased coverage. Diversity gain: Improved quality. Spatial multiplexing: Increased spectral efficiency. Additional transmission pipe: Increased data rates.

36 MIMO principle MIMO works well, when: 1) conditions are bad: no LOS signal component (or polarization separation) lot of scatteres 2) antennas have sufficient spacing uncorrelated antennas independent CIRs

37 Capacity ρ = SNR h = channel impulse response H = channel impulse response MxN (input, output antennas) matrix r = matrix rank

38 Rx diversity (SIMO) s h 1 w * 1 RX TX h Nr n 1 r 1 + ŝ w * NR n Nr r NR sˆ 1 * * T [ w K w ] = w r = 1 N R M rn r R r = h s + n

39 Tx diversity (MISO) TX Encoder RX

40 Tx Diversity (open loop), Rel. 6 (MISO) 2 Tx antennas improved quality & coverage support is mandatory for all Rel.6 compliant UEs Node B * * UE for QPSK

41 Closed loop Tx diversity Spread/scramble w 1 CPICH 1 Ant 1 DPCCH DPDCH DPCH Ant 2 w 2 CPICH 2 w 1 w 2 Weight Generation UE Determine FBI message from Uplink DPCCH

42 MIMO h 1,1 s 1 h 2,1 r 1 ŝ 1 TX h 1,2 n 1 RX s 2 h 2,2 r 2 ŝ 2 n 2 H sˆ sˆ 1 2 = H r s = s + H n r = r r 1 2 = h h 1,1 2,1 h h 1,2 2,2 s s n n 1 2

43 max MIMO capacity C W = { N, N } min log2(1 + T R min N R { N, N } T R S N )

44 MIMO & HOM relation MIMO can be considered as a form of HOM 2 streams of 4QAM = 1 stream of 16QAM

45 So many antennas

46 So many antennas

47 So many antennas

48 MIMO introduction into 3GPP 3GPP Rel. 5 3GPP Rel. 6 3GPP Rel. 7 & 8 HSDPA EUL TxD Transmit Diversity MIMO for HSDPA MIMO for R99 LTE UL SC-FDMA OFDMA MC-WCDMA DL OFDMA MC-WCDMA MIMO mandatory MIMO mandatory FDD only

49 HSDPA MIMO Where it s hot: higher isolation between cells and/or non-uniform load distribution: URBAN MICRO PICO & INDOOR Where it s not: uniform load distribution, frequency reuse of one, high load and little isolation between cells: URBAN MACRO

50 HSDPA + MIMO 3GPP Release 7 still open (LTE is also part of Rel. 7) 11 proposals MIMO up to 4x4 achievable data rate < 45 Mbps * (channel capacity < 80 Mbps *)

51 HSDPA + MIMO 3GPP TR Per-antenna rate control 2. Rate-Control Multi-Paths diversity 3. Double Space Time Transmit Diversity with Sub-Group Rate Control 4. Single Stream Closed loop MIMO with 4 Tx and L Rx antennas 5. Per-User Unitary Rate Control 6. TPRC for CD-SIC MIMO 7. Selective Per Antenna Rate Control 8. Double Transmit antenna array (D-TxAA) 9. Spatial Temporal Turbo Channel Coding 10. Double Adaptive Space Time Transmit Diversity with Sub-Group Rate Control 11. Single & Multiple Code Word MIMO with Virtual Antenna mapping

52 Ericsson MIMO Proposal Selective per-antenna rate control (S-PARC) Spreading Code 1 Antenna 1 Spreading Code 2 Scrambling Code High speed data stream D E M U X Coding Interleaving Mapping... Coding Interleaving Mapping Spreading Code C Scrambling Code Antenna T separately encoded data streams are transmitted from each antenna with equal power but with different data rates adaptively selects the number of antennas

53 And the winner is Primary transport block HS-DSCH TrCH processing w 1 w 2 CPICH 1 Ant 1 Spread/scramble w 3 Secondary transport block HS-DSCH TrCH processing w 4 Ant 2 CPICH 2 Primary: Always present for scheduled UE Secondary: Optionally present for scheduled UE w 1 w 2 w 3 w 4 Weight Generation Determine weight info message from the uplink Double Transmit antenna array (D-TxAA) LG Electronics